Normally aspirated strange power curve issues
 

Please see attached dyno sheet.

These are from two different cars. One is a '90 with a '01+ swap, DIYPNP & VVTuner. One is a '95 with a '01+ swap, DIYPNP & VVTuner. Both are running the same timing map, but different fuel maps as the '90 is running the '01+ injectors @ 60psi vs the '95 running the '95 injectors @ 45psi. Both have similar intakes. The '90 is running a Jackson Racing header, and has the VCTS butterflies still intact and working. The '95 has a Racing Beat header and the VCTS butterflies removed. The '90 is running a Jackson Racing high flow cat and a 1.6 Mazdaspeed Spec Miata exhaust. The '95 is running the Springfield Dyno Spec Miata exhaust. Same dyno, different days, similar conditions.

The overall power numbers are close.
'90:
RUN 91
HP 135.94
TQ 128.88

'95:
RUNS 25,33-35
HP 137.22
TQ 127.15

The issue I have is the shape of each curve. The '90 graph peaks @ 6,000 and falls off very fast. The '95 peaks 500 RPMs later @ 6,500 and by 7,000 is about 10hp stronger. The torque curves show a similar trend, the '90 makes more average torque, but falls off quickly after 6,000 and by 7,000 is almost 10ft/lbs lower. What would cause the '90 to fall off so fast?

VCTS butterflies?
Exhaust restriction compared to the '95?
Difference in the VVTuner maps?
Difference between the Jackson Racing header vs the Racing Beat header?
D. All of the above?

What say you?
Attachment 68885

Post an image of the dyno charts, nobody wants to download a PDF and look at it sideways.

How lazy can you be? It took me all of 1 second to rotate it 90*. Maybe 2 seconds to download the PDF.

If you are working 14-16 hours per day, 7 days a week, 2 seconds here and there quickly add up to time you don't have.

No one is going to review this until you stop acting like a Democrat.

American dream post.

While I can understand this to an extent (I work 50 hour weeks on top of 3 on campus master's courses all while trying to get my new business up an running) I still think the effort I put it was minimal at best.

Thread drift guys... Not into politics, just finding out why my car loses so much power up top!

Swap IMs, go back and dyno, and find out if that's the cause.

The two cars are different. Different parts, different tunes, different motors.

Why do you think there are Sooo many posts about "i have the same parts and motor but so&sos map doesn't work for me..."

were these cars dyno tuned?

The '90 was tuned on the Dyno. The '95 was just a baseline using the spark map from the '90 and an adjusted fuel map before these baseline runs.

Do they have identical VVT maps?
Were they dyno tuned?
It can have a profound effect on the shape of the torque curve.

If some people are to be believed, the VTCS butterflies are a significant restriction at the topend - however I would expect it to depress the peak power number, and not just cause a dropoff after peaking.

VVT maps are the same.

VVT maps are both as delivered in the VVTuner. I am wondering if the PID settings in the VVTuner software need to be adjusted. While both VVTuners are calling for the same amount of retard/advance one might be getting more or less. I will be looking into this on the dyno.

I am picking up the exhaust that was used on the '95 and I will be putting it onto my '90 and going back to the dyno sometime this week. Once I have it strapped to the dyno and I make a few runs I will see what happens with the curve. If I do not see any changes up high, I will open the VVTuner software and adjust the curves up high and see what happens.

Once I get these results, I am planning on fitting a VICS manifold on the motor and adjusting the DIYPNP to switch the VICS @ 5,500rpms and head back to the dyno.

Thanks for everyone's help so far.

Sounds like a plan, but I don't think advancing vvt up top will yield anything for you. Pretty sure people reported it basically only working in the lower rpm, sub 5k or so

That is correct, the VVT should be letting the intake cam go fully retarded up top. The VVTuner map is calling for 5 degrees of advance based on the table above 6,000rpms.

The PID's in the VVTuner software might need to be adjusted. I might be requesting say 5 degrees of advance up top, but getting 10 etc. Adjusting the PID's might be the answer if the the target and the actual advance are different.

Here is a view of the VVTuner map.
https://www.miataturbo.net/attachmen...ine=1362588880

I got over to the dyno this weekend, but was not able to test the exhaust. The exhaust from the '95 hit the axle and one of the bolts for my seat mounts on my '90.

I was able to do some testing on the VVT tuning and saw no gains up high. I moved on to testing my intake. I removed the filter from my intake and made a run, no change. I removed the intake piping and saw a power drop almost everywhere. Now, here is where it gets interesting.

I took my intake piping off, mine is the same size as the throttle body, either 2.25" or 2.5" and I put the intake from the '95, which is 3". I saw a gain up high of about 3-4 HP, but also saw a 10ft/lb loss down low. So if you want more torque down low, go smaller on the intake tube... lol.

The printer at the dyno was broken, so I do not have the graphs. I am going to try to swing by with a flash drive and get the graphs.

Holy restrictive intake Batman!

I found my power loss above 6k! I was able to swap to a VICS manifold from the VCTS manifold with butterflies. I found 14HP and 10ft/lbs at 7200! I lost 2-3 HP and torque everywhere else.

Attachment 72955